The present invention relates to wind turbines used to convert wind energy into mechanical energy, more specifically, vertical-axis turbines. Vertical-axis turbines are typically of a long axis type, allowing large columns of air to be harnessed. These devices differ from horizontal-axis (propeller) type windmills which typically pivot about a vertical axis in order that they may face directly into a wind. The present invention more specifically relates to vertical-axis turbines designed to be employed as a cost effective alternate power source in any wind condition.
Wind as a source of energy is a concept that has been promoted for some time. According to one source, there is evidence which shows that windmills were in use in Babylon and in China as early as 2000 B.C. The U.S. Patent and Trademark Office has granted patents on windmill devices dating back to the early to mid 1800's. Despite the continued research and development in this age old technology, until the present invention, no windmill or wind turbine device has successfully appropriately addressed some of the most important problems which have seemingly made the harnessing of wind not economically feasible. While wind is unquestionably a large potential source of energy, estimated to be about 5 kW per acre in the United States, its variability in velocity has made it an unreliable source. Many devices such as U.S. Pat. No. 4,850,792 to Yeoman, U.S. Pat. No. 4,035,658 to Diggs and U.S. Pat. No. 2,406,268 to Terhune have relied on the ability of concentrating low to moderate winds for producing power. Others, like those shown in U.S. Pat. No. 4,834,610 to Bond and U.S. Pat. No. 4,075,500 to Oman, et al. (a horizontal-axis turbine), have accomplished the harnessing variable wind speeds by using modern variable speed governors. No device currently known to the present inventors is capable of adequately harnessing low and high-winds for power production. High winds are characterized, for purposes of discussion as currents having average velocities above 45 m.p.h., or having gusts greater than 60 m.p.h. Many devices are designed to fold and/or feather in winds reaching certain levels. Such devices are illustrated in U.S. Pat. No. 4,818,181 to Kodric, U.S. Pat. No. 4,632,637 to Traudt, and U.S. Pat. No. 3,942,909 to Yengst. These techniques, while intended to protect the structural integrity of the windmill, decrease a device's ability to produce power. Others, such as U.S. Pat. No. 5,391,926 to Staley and Elder, attempt to harness high winds emanating from any direction for power production but low to moderate winds have been unable to produce adequate torque for continual reliable power generation. Until the present invention variable winds have been an untapped source of energy by those skilled in the relevant art.
In the past, wind driven power generators of all sorts have attempted to harness the energy present in the wind. Some have concentrated their efforts in the low to moderate wind range and suffer periodic damage from the occasional high wind while others work well in the moderate to high wind range with little or no success in harnessing low speed wind. No prior art has effectively drawn useable power from the slight breeze all the way to gale force winds. Perhaps one of the biggest reasons for the lack of all wind turbines has to do with the structural integrity of typical wind devices. By design many are lightweight, inadequately supported, and made from insufficient materials. A number of these devices are comprised of a multitude of moving parts, such as rotors, stators, vanes, shields, and the like. These parts not only compromise the integrity of the machine, but also require continuous maintenance, repair and/or replacement. For such a device, which may produce only a few kilowatts of power, the costs soon begin to outweigh the benefits. Another concept widely used is to build large multi-story wind turbines capable of producing at or near the megawatt level. Two such devices are shown in U.S. Pat. No. 3,902,072 to Quinn, and U.S. Pat. No. 3,994,621 to Bogie. It is believed that these devices would cost close to $100 million to build and several hundred thousand to maintain each year. Another example is the 1.25 MW generator installed near Rutland, Vermont. This is believed to be the largest windmill ever built in the United States, having two main blades each 175 feet in diameter. This facility operated intermittently between 1941 and 1945, during the war years when most resources were being used for war efforts. In 1945 one of the blades broke due to material fatigue and was never repaired, presumably due to a lack of cost efficiency. Similar to the smaller units, these large devices become cost prohibitive on a much larger scale. The present invention solves this second problem by presenting a low cost, low maintenance, cost efficient wind turbine. While certain aspects of the design have been known, until the present invention the proper combination of elements, new and old, has not been achieved to provide a commercially viable product.
Variable wind velocity is not, of course, the only obstacle in harnessing kinetic energy from the wind. Wind direction has been another area of study and development. Wind currents are typically unpredictable, and due to topography, upper air disturbances, changing weather patterns, or seasonal variations, they rarely blow in the same direction for any substantial length of time. For this reason effective wind machines must be capable of immediately accommodating winds from a full 360 degrees. Some devices have attempted to accomplish this goal with pivoting shields, and stators or wind directing vanes. U.S. Pat. No. 4,474,529 to Kinsey, U.S. Pat. No. 537,494 to Stevens et al., the Yengst patent, and many other devices illustrate such an approach. As mentioned previously, additional moving parts usually detract from a machine's cost effectiveness. While not in the field of the present invention horizontal-axis machines typically pivot the entire rotor assembly so that it may face upwind. Still other designs leave the rotor assembly open (that is, no wind directing vanes or stators are utilized) so that winds from any horizontal direction may impart rotation upon the rotor assembly. This leaves the rotor completely open to the harshness and destructive abilities of the wind. Once again the present invention solves this problem by providing 360 degrees of wind reception, in all types of wind conditions.
The present invention, in its various embodiments, recognizes and addresses these and other problems and overcomes many limitations encountered by those skilled in the art. Many devices and procedures have taught the use of folding or feathering in high wind conditions, and thus have been unable to realize the potential power of high winds. Others, such as the Staley and Elder patent have attempted to address the damaging characteristics of high winds by stressing structural integrity and durability to the point of sacrificing the ability to produce adequate torque in the low to moderate wind speed range. It is not economically feasible to build a wind turbine that can only produce mechanical power during periods of high wind. The entire range of wind conditions must be fully utilized for a wind turbine to be commercially viable. Problems such as high cost and high maintenance of most wind energy facilities exist in the field, but such problems have not been adequately addressed by those skilled in the art. While high velocity wind is a well known natural occurrence with high kinetic energy, its value in the field of vertical-axis wind turbines has not only been ignored to some extent, it has often been looked upon as a detriment. The prior art has taught away from the present invention by stressing rotor attachment and stator curvature. Rather than supplying a system which affords only an incremental increase in performance over the prior art, the present invention utilizes techniques which were not previously considered in order to achieve what may perhaps be leaps in performance compared to the prior art. Further, the present invention has achieved a more full utilization of a previously untapped precious natural resource, the wind.